We are planning to continue with our studies on host-coccidia relationships by studying methods of penetration utilized by sporozoites and merozoites. This will be accomplished by means of scanning and transmission electron microscopy. We will investigate also the effects of parasites on the nuclear structure of the host. We will explore the possible use of invertebrate chemosterilants such as alkalating agents and antimetabolites and derivatives of S-triazine and phosphoric triamide for the control of coccidia. This objective will be tested, however, only after studying the structural changes (if any) induced by these chemicals in both host and parasites in vivo and in vitro. We are planning to study the process of fertilization and its controlling factor(s) utilizing several approaches: a) detection of parthenogenicity by inhibiting microgametogenesis with known spermicides such as TLCK, TPCK, and others; b) fertilization of macrogamonts in vitro by introducing microgametes in the vicinity of macrogamonts with micromanipulators; and 3) determine whether or not the macrogamete-microgamete attachment is found to occur prior to fertilization.